This invention relates in general to electrostatography and, in particular, to an electrostatographic imaging member having an outer imaging layer comprising a high molecular weight polysiloxane dispersed in a film forming polymer matrix.
In electrophotography, an electrophotographic plate containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging its surface. The plate is then exposed to a pattern of activating electromagnetic radiation such as light. The radiation selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided toner particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the electrophotographic plate to a support such as paper. This imaging process may be repeated many times.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. One type of composite imaging member comprises layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. In U.S. Pat. No. 4,265,990, a layered photoreceptor is disclosed having separate photogenerating and charge transport layers. The photogenerating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
Other composite imaging members have been developed having numerous layers which are highly flexible and exhibit predictable electrical characteristics within narrow operating limits to provide excellent images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, a charge transport layer and a conductive ground strip layer adjacent to one edge of the imaging layers. This photoreceptor may also comprise additional optional layers such as an anti-curl back coating and an overcoating layer.
Electrostatographic imaging members are generally exposed to repetitive electrostatographic cycling which subjects exposed layers thereof to abrasion and leads to a gradual deterioration of the mechanical and electrical characteristics of the exposed layers. For example, repetitive cycling has adverse effects on exposed surface of the outer imaging layer of the imaging member, such as the charge transport layer, charge generating layer, overcoating layer, electrographic imaging layer and the like. When blade cleaning is utilized to remove residual toner particles from the imaging surface of photoreceptors, particles often adhere to the imaging surface and form comet shaped deposits during cycling. These deposits cannot be readily removed by blade cleaning and appear as undesirable defects in the final print output.
It has also been discovered that glue particles from wrappers utilized for packaging copy paper often accumulate on the photoreceptor surface and cannot be readily removed by cleaning blades. These deposits form black spots on the final print output. In addition, paper fibers cling to the imaging surface and cause print-out defects which appear black spots.
Also, the high contact friction which occurs between the cleaning blade and the imaging surface tends to wear both the blade and the imaging surface. Reduction in charge transport layer thickness due to wear increases the electrical field across the layer thereby increasing the dark decay and shortening the electrophotographic service life of the imaging member. Attempts to compensate for wear of the imaging surface by increasing the thickness of charge transport layers cause a decrease in the electrical field which then alters the photoelectric performance and degrades the copy printout quality which, in turn, require more sophisticated equipment to compensate for the thicker charge transporting layer. Moreover, the change in transport layer thickness as it wears away alters the electrical properties of the photoreceptor and consequently alters the quality of images formed. Attempts have been made to overcome these problems. However, the solution of one problem often leads to additional problems.